The Parasitic Wood Wasps, family Orussidae, are grouped with the sawflies. Orussids are rare—there are only nine North American species—and not well known. They’re rarely seen in the field, let alone photographed. The larvae appear to be parasites on wood-boring beetle larvae (Family Buprestidae). There are two species in the northwest United States.
See ID link above for diagnostic characteristics and movies.
In these locations, I saw two morphs, one with a red abdomen and one with a black abdomen with a white marking near the tip of the abdomen.
You can read comments on my Bugguide.net pages on Orussus.
I photographed many of these Parasitic Wood Wasps on the beach south of Marlyn Nelson County Park in Sequim, WA (See Clallam County Parks web page). The park is an east-facing salt-water beach on Sequim Bay, with a marsh directly inland of the southern part. I only saw these wood wasps on a few driftwood logs above the high-tide line and adjacent to the marsh. I also photographed Parasitic Wood Wasps in a second location, the mouth of the Elwha River, a freshwater beach.
In both locations, they only occurred on logs with nearly identical circular holes, perhaps old holes originally made by common buprestids in our area. Orussus appears to hide in these holes. You can see one backing into a hole in image 5 and a video on the ID and video page. In image 6, an Orussus is peeking out of the hole.
They were quite difficult to photograph, dashing along the log and switching direction suddenly. They looked from a distance like large ants. Every once in a while one would appear to disappear, their takeoff was so quick.